For 3a, find the midpoint of PQ. Then, find the line passing through PQ with a slope equal to the negative reciprocal of the slope of PQ.

For 3b, find the equation of the line, then solve with 3a.

Step-by-step:

The midpoint of PQ = (6, 2), and the slope is -4/3.

3a passes through (6, 2) and has a slope of 3/4.

y = (3/4)x - 5/2

The line passing through (20, 2) with a slope of -1/8 is

y = (-1/8)x + 9/2

The intersection of these lines:

(3/4)x - 5/2 = (-1/8)x + 9/2

(7/8)x = 7

x = 8

y = (-1/8)(8) + 9/2

y = 7/2

(8, 7/2)